Interpretive Summary: Codling moth is a key pest of apple, pear, and walnut and several formulations of sex pheromone, principally hand-applied dispensers, are widely used by growers to manage codling moth. Researchers at the USDA, ARS, Yakima Agricultural Research Laboratory, Wapato, WA developed a low volume spray application of a microencapsulated sprayable formulation that increased its effectiveness compared with a standard high volume spray application. Studies were conducted to test our hypothesis that the low volume spray creates thousands of attractive leaves that would compete with virgin females for male moths. Indeed, several studies showed that clustering of microcapsules does create attractive leaves and that leaves can remain attractive for several weeks. Studies showed that microcapsules deposited on the top surface of leaves have a shorter residual period of activity and precipitation can also reduce the residual attractiveness of leaves. These results support further studies aimed to refine the use of low volume pheromone sprays to create larger numbers of longer lasting and more attractive point sources that will further enhance mating disruption of codling moth.

Technical Abstract:
Studies were conducted to examine the depositioin of microcapsules and the attractiveness of treated apple leaves for codling moth, Cydia pomonella (L.), following low volume concentrated sprays of a microencapsulated (MEC) sex pheromone formulation (CheckMate CM-F). Nearly 30% of leaves collected from sprayed zones within tree canopies had no microcapsules while 20% had >20 microcapsules. Microcapsule density was correlated with leaf area and significant differences inthe density of microcapsules per leaf were found due to both height and depth in the canopy relative to the sprayed zone and leaf surface. In general, the highest concentration of microcapsules was deposited on the underside of leaves in the sprayed zone. However, deposition was greater on the upper than the bottom surface of leaves in the canopy below the spray zone and in the tops of trees on the opposite side of the canopy. Field-aged MEC-treated apple leaves elicited upwind flight and moth contact in flight tunnel tests for at least 5 weeks. Precipitation reduced the attractiveness of leaves, particularly for leaves treated only on their upper versus bottom surface. Traps in unsprayed orchards baited with MEC-treated artificial leaves were attractive for 5 weeks. Moth catches in similar traps placed in MEC-sprayed plots were low but increased significantly over 3-4 weeks. These data suggest that following a brief initial period of sensory disruption, low volume MEC sprays create point sources of sex pheromone (leaves) within the orchard that may enhance mating disruption via competitive attraction.